The invention relates to associations of immiscible polymers by virtue of the use of a compatibilizing agent also called an emulsifier.
In recent years the literature has extensively described both the advantage of associations of polymers and the problems presented by the use of polymers that are immiscible with each other and the solutions provided by the compatibilizing agents.
In general, these compatibilizing agents themselves consist of polymers, homo- or copolymers, carrying sites or groups permitting the adhesion to the polymers to be associated, these groups being generally either incorporated directly into the chain by polymerization or attached chemically to these compatibilizing polymers (chemical reaction between functional sites, copolymerization, grafting).
Purely by way of illustration of such compatibilizing agents it is possible to mention polystyrene and polycaprolactone block copolymers (Henschen and Teyssie, Polymer, Vol. 31, Aug. 1990 pp. 1473-80), polypropylene graft polycaprolactone which is then, after hydrolysis, modified with .epsilon.-caprolactone (Chung, Macromolecules, Vol. 27, 1994 pp. 1313-19), copolymers of styrene/maleic anhydride/unsaturated derivatives modified with caprolactone (JP-A-03.052.952) and .epsilon.-polycaprolactone graft maleic anhydride (JP-A-03.188.160).
Other compatibilizing agents consist, for example, of polyolefins modified with an unsaturated carboxylic acid (FR-A-2.107.538), copolymers of an olefin or of styrene and of an unsaturated mono- or dicarboxylic acid or an ester or an anhydride of this acid (FR-A-2.200.321), a graft copolymer consisting of at least one monoamine polyamide oligomer and of an .alpha.-monoolefin polymer or copolymer grafted with a monomer that can react with the amine functional group of the oligomer (FR-A-2.626.090), a di- or triblock copolymer consisting of at least one N-vinylpyrrolidone telomer or of methyl methacrylate and of an ethylenically unsaturated polymerizable mono- or difunctional oligomer or of a polycondensable monomer or of a lactam (FR-A-2.616.151) or a block copolymer of polymethyl methacrylate and of polycarbonate (U.S. Pat. No. 4,319,003).
In general, these compatibilizing agents have a chemical structure such that it permits an at least partial miscibility of this agent with the polymers to be compatibilized.
In most cases, obtaining this chemical structure and the insertion of sites promoting at least this partial miscibility in the same polymer backbone (often called backbone polymer or copolymer) requires a group of chemical reactions which are complex and all the more laborious since the chemical structure of such an agent must be closely adapted to the nature of the polymers to be associated. Thus, in general, a compatibilizing agent for the polyamide/polypropylene pair will not fulfil the same compatibilizing function with the PVDF/polyolefin pair.